In the treatment of diseases such as cancer, certain types of cancer cells have been found to denature at elevated temperatures which are slightly lower than temperatures normally injurious to healthy cells. These types of treatments, known generally as hyperthermia therapy, typically utilize electromagnetic radiation to heat diseased cells to temperatures above 41° C. while maintaining adjacent healthy cells at lower temperatures where irreversible cell destruction will not occur. Other procedures utilizing electromagnetic radiation to heat tissue also include ablation and coagulation of the tissue. Such microwave ablation procedures, e.g., such as those performed for menorrhagia, are typically done to ablate and coagulate the targeted tissue to denature or kill it. Many procedures and types of devices utilizing electromagnetic radiation therapy are known in the art. Such microwave therapy is typically used in the treatment of tissue and organs such as the prostate, heart, and liver.
One non-invasive procedure generally involves the treatment of tissue (e.g., a tumor) underlying the skin via the use of microwave energy. The microwave energy is able to non-invasively penetrate the skin to reach the underlying tissue. However, this non-invasive procedure may result in the unwanted heating of healthy tissue. Thus, the non-invasive use of microwave energy requires a great deal of control. This is partly why a more direct and precise method of applying microwave radiation has been sought.
Presently, there are several types of microwave probes in use, e.g., monopole, dipole, and helical. One type is a monopole antenna probe, which consists of a single, elongated microwave conductor exposed at the end of the probe. The probe is sometimes surrounded by a dielectric sleeve. The second type of microwave probe commonly used is a dipole antenna, which consists of a coaxial construction having an inner conductor and an outer conductor with a dielectric separating a portion of the inner conductor and a portion of the outer conductor. In the monopole and dipole antenna probe, microwave energy generally radiates perpendicularly from the axis of the conductor.
Because of the perpendicular pattern of microwave energy radiation, conventional antenna probes are typically designed to be inserted directly into the tissue, e.g., a tumor, to be radiated. However, such typical antenna probes commonly fail to provide uniform heating axially and/or radially about the effective length of the probe.
It is especially difficult to assess the extent to which the microwave energy will radiate into the surrounding tissue, i.e., it is difficult to determine the area or volume of surrounding tissue which will be ablated. Furthermore, when conventional microwave antennas are inserted directly into the tissue, e.g., cancerous tissue, there is a danger of dragging or pulling cancerous cells along the antenna body into other parts of the body during insertion, placement, or removal of the antenna probe.
One conventional method for inserting and/or localizing wires or guides is described in U.S. Pat. No. 5,221,269 entitled “Guide for Localizing a Nonpalpable Breast Lesion” to Miller et al. which is incorporated herein by reference in its entirety. Miller describes a wire guide which is delivered into breast tissue through a tubular introducer needle. When deployed, the wire guide cuts into and scribes a helical path about the tissue distal to a lesion while the remainder of the distal portion of the wire guide follows the path scribed by the distal tip and locks about the tissue. However, Miller does not teach any structures for curved microwave antennas or their methods of use for surrounding predetermined regions of tissue for treatment.
U.S. Pat. No. 5,507,743 entitled “Coiled RF Electrode Treatment Apparatus” to Edwards et al., which is incorporated herein by reference in its entirety, describes an RF treatment apparatus for hyperthermia at low temperature which is also able to effect microwave treatment via an RF indifferent electrode which forms a helical structure. However, the electrode, which is deployed from an introducing catheter, comprises a hollow tubular structure with fluid ports defined along the structure.
Accordingly, there remains a need for a microwave antenna which overcomes the problems discussed above. There also exists a need for a microwave antenna which can be inserted into tissue and which produces a clearly defined area or volume of ablation. Moreover, there is also a need for a microwave antenna which can ablate an area or volume of tissue without ever having to directly contact the ablated tissue.